French rocker Johnny Hallyday's decision to press ahead with his concert in Brussels on Saturday despite security concerns was met with a deafening roar of approval from fans seeking respite from a traumatic week.

The 72-year-old singer, known as France's answer to Elvis Presley, highlighted his Belgian roots as he took to stage for the latest leg of his "Staying Alive" tour, delighting a sold-out crowd determined to have a good time after the horror of Tuesday's airport and metro attacks.

"Part of my blood is French through my mother and the other part is Belgian through my father," he told the 11,000-strong audience, which responded with chants of "Johnny, Johnny, Johnny!"

In a still shell-shocked nation, fans said the concert was their way of showing they would not give in to fear.

"If we give in to panic, we'd never go anywhere anymore. I'm not worried, I trust the security services and... Johnny!" said Lindsey, enjoying the music with a beer in her hand.

Coming just four days after Belgium's worst-ever terror attacks, which left 31 dead, security at the gig was boosted significantly, with police and even soldiers deployed at the Palais 12 venue.

"We have tripled the number of staff and are have police and army reinforcements," Stefan Feldbusch, security coordinator at Palais 12, told AFP. "Everyone is being searched, which is not necessarily the case usually."

In stark contrast to Hallyday, US pop star Mariah Carey has cancelled her upcoming gig in the wake of the attacks, citing security fears.

Living up to the old adage that the show must go on, Hallyday kicked off his gig in typically flamboyant fashion, stepping out of a giant skull as red lasers and smoke filled the stage, to loud cheers from the audience.

Clad in his trademark leather trousers and wearing sunglasses, France's favourite rock 'n' roller then belted out some of his biggest hits, including "Gabrielle" and "Quelque chose de Tennessee".

Brussels resident Michel, wearing a Johnny Hallyday T-shirt, said he had come to the concert to "forget this terrible week".

"When you see Johnny, you're not afraid anymore."

While Hallyday has never achieved widespread fame abroad, he is a musical icon at home and has sold more than 100 million records in his decades-long career.

In a sign of the ageing star's enduring appeal, Saturday's performance was broadcast live in some 300 cinemas in France.